Differentiating True Occlusion from Pseudo-Occlusion: The Role of Extended Multiphase Computed Tomography Angiography Scan Range in Internal Carotid Artery Occlusion.

Background: Accurate localization of internal carotid artery (ICA) occlusion is critical for optimizing endovascular thrombectomy (EVT) strategies. Conventional multiphase CT angiography (mCTA) often omits the carotid bifurcation in delayed phases, limiting differentiation between true cervical ICA occlusion and pseudo-occlusion. Methods: We retrospectively analyzed 56 acute ischemic stroke patients with ICA occlusion who underwent EVT and extended-range mCTA between 2016 and 2020. The scan range of the second and third arterial phases was modified to include the carotid bifurcation. Imaging patterns were evaluated to distinguish bifurcation stenosis with superimposed occlusion from proximal ICA occlusion, and to infer thrombus location by comparing arterial opacification levels across phases. Results: Extended mCTA significantly improved visualization of ICA enhancement patterns in delayed phases (p < 0.001). Cases with bifurcation stenosis showed consistently lower and stable opacification levels across phases, whereas proximal ICA occlusion demonstrated progressive contrast advancement. Distal occlusion, particularly beyond the ophthalmic artery, showed higher opacification. Including the carotid bifurcation increased scan length by ~10%, with acceptable radiation exposure. Conclusions: Incorporating the carotid bifurcation into delayed mCTA phases enhances the ability to differentiate occlusion subtypes and estimate thrombus location. This refined imaging approach enables better EVT planning, including device selection and procedural timing, thereby improving patient outcomes in acute stroke care.